~ 100 Words on the Parsha - Shimini

Moshe became angry at Elluzar and Issumar, the sons of Aharon and asked “Why did you not eat the קרבן פסח in the holy place … Hashem gave it to you to bring forgiveness for the sins of the Jews.”

Normally the Torah does not give a reason for the performance of a Mitzva. A person must do the Mitzva simply because he was commanded by Hashem. Here, however, Moshe Rabbanu is questioning the reasoning for the קרבן פסח in its proper place. He tells the Cohanim that the reason for this Mitzva is to bringכפרה to the Jews.

These פסוקים appear after the death of Nuduv and Avihu, who performed a Mitzva improperly. An improperly performed Mitzva does not bring a כפרה to the Jews. Moshe Rabbanu wanted to ensure that Nuduv and Avihus Avara would bring a כפרה.